Various systems use transponders to identify objects from a distance by associating a transponder with the object. The transponders, also known as radio frequency identification (RFID) tags, are typically programmed with unique identification codes that identify the object. FIG. 5 illustrates a conventional tag and reader system. A reader 510 may include an inductive element 512 generating a magnetic field that energizes a tag 520. The tag 520 may include an inductive element 522 and a load 524. When the tag 520 is in proximity of the reader 510, the magnetic field generated by the reader 510 energizes the tag 520 by inducing a voltage across the inductive element 522.
The tag 520 may transmit limited information back to the reader 510, such as an identification code. For example, a load 524 shunted across the inductive element 522 when the tag 520 is energized causes the magnetic coupling between the reader 510 and the tag 520 to change. The change in the magnetic coupling results in voltage fluctuations across the inductive element 512 of the reader 510, which when demodulated identifies the information exchanged between the tag 520 and the reader 510.
Readers and tags, such as shown in FIG. 5, are used for a number of applications. However, these applications are usually limited to remote identification applications.